Design Balcony

A balcony is a hole punched deliberately through everything the wall was built to do. Structure crosses the insulation, waterproofing has to turn up beside a door that has to be level for accessibility, and a guard fixes into whatever is left. It is a small element that fails in four ways at once.

Workflow

Step 1. Establish what is underneath, first

Ask, in one message:

1. What is under the balcony: open air, occupied space, a garage, another balcony?
2. What is the wall behind it? Point at design-wall-assembly.
3. What structure is proposed or possible?
4. What door, and is it on the accessible route? Quote the threshold provision if so.
5. Quote the code's guard requirements and its drainage provisions.
6. Who uses it, and for what: standing, sitting, planting, storage, a barbecue?
7. How is it maintained and cleaned, and can the underside be reached? Point at facade-access-study.

Question 1 changes what this is. Over occupied space it is a roof with a guard on it, and it gets design-roof-assembly and design-below-grade-assembly's level of care. Over open air a leak is a nuisance; over a bedroom it is a claim.

Step 2. Settle the structural relationship, because everything follows it

Three options and they are different buildings:

Relationship	What it means	What it costs
Continuous slab	The floor slab runs straight out	Cheapest to build, worst thermal bridge on the building, and the slab edge is cold inside
Thermally broken connection	A proprietary connector at the line of insulation	Continuity kept, a structural component with a lead time, and the engineer specifies it
Independently supported	Posts, hangers, or a separate frame	The envelope stays whole, and there is now a second structure with its own foundation and its own movement

State which and why. Then say what it does to the four control layers, because the answer is different for each. Point at design-wall-assembly for the layers and to the engineer for the connection.

If the answer is a continuous slab, say plainly that the thermal bridge is unquantified and that condensation-check should run on the slab edge inside. That is where the condensation and the mould appear, in the corner of the room behind it.

Step 3. Work the falls and the threshold together

They fight each other and both are non-negotiable:

• The surface has to fall away from the building.
• The door threshold has to be low, and on an accessible route it has to be very low, quoted from the standard.
• The waterproofing has to turn up behind the door, high enough to matter.

Those three demands meet at one line. Report the strategy: a recessed structure so the finished level drops, a drainage channel across the door, a raised pedestal system over the waterproofing, or a combination. Say what each costs in structure and in build-up depth.

A balcony detailed with the threshold as an afterthought is the single most common source of water inside.

Step 4. Work the drainage and where the water goes

• Where does the water leave: a drain, a scupper, an open edge?
• An open edge means water runs down the facade below. Say so; it stains, and on a multi-storey building it stains the same place repeatedly.
• If there is a drain, where does the pipe go, does it pass through occupied space, and what happens if it blocks? Point at design-roof-drainage.
• What happens in a freeze: standing water, ice at the door, a blocked outlet.
• Where the water goes at the bottom of the building.

Step 5. Work the guard, which fixes into the weakest place

• What the guard fixes to: the slab top, the slab edge, the face, or a separate post. Each is a different penetration of the waterproofing.
• Every fixing through a waterproof surface is a hole. Name what closes each one, and prefer a fixing that does not pass through the membrane at all.
• Whether the guard is structural to a load quoted from the code, which is the engineer's.
• What the guard does to the elevation and to the view from inside, sitting.
• Drainage at the base of the guard, so water does not pond against it.

Step 6. Work the underside and the edges

• What the soffit is, and whether it is insulated. Over occupied space it has to be.
• Where the balcony meets the wall at each end, and what the control layers do there. Point at design-window-perimeter for the door.
• Where it meets the balcony above and below.
• Any planter, which is a permanently wet weight over the waterproofing.
• Anything fixed to it later by an occupant: an awning, a light, a hook.

Step 7. Report

• What is underneath, and therefore what standard of care applies.
• The structural relationship, with what it costs the envelope.
• The falls and threshold strategy, and what it costs in depth.
• The drainage and where water goes, including the blocked case.
• Every guard fixing and what closes it.
• Every open value, with who supplies it.
• The hand-offs: engineer for the structure and the guard load, condensation-check for the slab edge, facade-access-study for maintenance.

Close by saying the thermal bridge has not been quantified.

Step 8. Save, if asked

Ask whether to write the detail to a file and where.

Rules

• Never supply a dimension, a load, a thermal value, or a guard height.
• Ask what is underneath before anything else.
• Settle the structural relationship before detailing.
• Work the falls and the threshold as one problem, never in sequence.
• Name what closes every fixing that passes through the waterproofing.
• Say where water goes at an open edge, and that it stains.
• Say on every run that the thermal bridge is unquantified.

Anti-patterns

• Detailing the threshold after the levels are set.
• A continuous slab with no mention of the cold slab edge inside.
• Guard posts through the membrane with the closure left to the contractor.
• An open drainage edge over an entrance or a principal elevation.
• Treating a terrace over occupied space as a balcony rather than as a roof.
• Recalling a guard height.
• A planter over waterproofing with no thought to weight, drainage, or the day it has to be lifted to find a leak.
• Forgetting that the underside is a soffit somebody sees.

Resources

None. This skill is one file. Output is written directly at the path you choose.